beyond the Wii U being marketed terribly at the start, releasing with a weak batch of games, AND conceptually being flawed (Gamepad is just ridiculous, the telltale sign of a great controller is it being SO well designed that you DONT have to look down at your lap/hands)- the issue with the Wii U ALSO is that there have been incredibly weak releases
limited big new IP (sorry but Wonderful 101 is glorfied shovelware, no matter how fun it is), Splattoon is about all you have. And extremely lacking in big Nintendo franchise releases.
where the hell was a Pokemon home console game? something like that pushes a LOT of sales for hardware because it convinces Pokemon handheld fans (which there are tonsss) to get the home consoel as well. Where was the pure Mario 3D title? sorry but 3D land does not have its own unique identity and feels more like an experiment. Where is the console exclusive Zelda or Metroid?
where are the mainline secondary popular franchise releases for things like Animal Crossing, F Zero, etc.?
people may not realize it but you can add a lot of sales by adding in some of these smaller franchises. Something like Animal Crossing or F-Zero can pull a lot of 'edge' Nintendo fans, who are uncertain on whether to pick up the system
and then some of the releases have just been mega disappointing, Mario Party = not good the last few iterations, etc.
overall the software for the WIi U was the weakest of any system of theirs since the Virtual Boy. People who claim 'Nintendo is done' aren't paying attention, they simply strategized terribly with the Wii U.
even with the bad marketing and dumb controller, if they had simply released a dedicated 3D Mario game (like a new Mario Galaxy) and like a mainline Pokemon game for home consoles- they probably could have sold like twice as many systems as they have. Same with a Zelda title earlier on. I would say that a huge amount of people interested in a Nintendo system are going to practically be in it specifically for a good 3D Mario, Pokemon, or Zelda. That's a lot of missed opportunitiy not genuinely having one of those for 4 years of the system
The good news is that we have plenty of explanation of WHY the Wii U has failed. Its not hard to see. Nintendo should know exactly what they need to do for the NX.
they should release the NX with a Pokemon game, a new Mario Galaxy game, and some random franchise reemergence like F-Zero- that will bring in the audience